Yarn weight #4

Medium weight yarn (#4)

Medium yarn is category 4 in the Craft Yarn Council system and includes worsted, afghan and aran yarns. Crocheters work medium yarn with a 5.5–6.5 mm hook, US I-9 to K-10½, at 11–14 single crochet per 4 inches. Medium worsted yarn is the most common choice for blankets and beginner projects.

By the crochetpatterns.io editorial team · Reviewed September 13, 2026 · Editorial policy

Medium yarn at a glance
Detail	Value
CYC number	#4
Also called	Worsted, Afghan, Aran, 10-ply (AU/NZ)
Crochet gauge	11–14 sc per 4 in / 10 cm
Hook size (mm)	5.5–6.5 mm
Hook size (US)	I-9 to K-10½
Yards per 100 g	about 150–220 yd
Best for	Blankets and afghans, Beanies, Granny squares, Beginner projects

What is medium weight yarn called in the US and UK?

Medium yarn is category 4 in the Craft Yarn Council system. You will also see it sold as worsted, afghan, aran, 10-ply (au/nz). It typically runs about 150–220 yd per 100 g, though the exact length depends on the fibre.

How does medium yarn compare with the weights either side?

Light (#3) is one step finer and works up at 12–17 sc per 4 in / 10 cm. Bulky (#5) is one step thicker at 8–11 sc per 4 in / 10 cm. Moving one weight up usually means going up about one to two hook sizes.

Medium yarn and neighbouring weights
Weight	Crochet gauge (4 in)	Hook (mm)	Hook (US)	Yards per 100 g
#3 Light	12–17 sc per 4 in / 10 cm	4.5–5.5 mm	7 to I-9	about 200–280 yd
#4 Medium	11–14 sc per 4 in / 10 cm	5.5–6.5 mm	I-9 to K-10½	about 150–220 yd
#5 Bulky	8–11 sc per 4 in / 10 cm	6.5–9 mm	K-10½ to M-13	about 80–150 yd

What hook size should you use for medium yarn?

Start with a hook between 5.5–6.5 mm (I-9 to K-10½). Standard hooks in that range are 5.5 mm (US I-9), 6 mm (US J-10), 6.5 mm (US K-10½). Go down a size for tighter fabric such as amigurumi, and up a size for drape.

What is medium yarn best for?

Medium yarn is a good choice for blankets and afghans, beanies, granny squares, beginner projects. Our library has 62 patterns in this weight, such as round amigurumi cat for beginners, little round amigurumi bunny with long ears, classic granny square, simple crochet leaf with stem, heat-safe double thickness crochet pot holder.